This invention relates to proximity sensors. In particular, the invention relates to capacitive sensors for sensing the presence or touch of an object adjacent to a sensor.
Capacitive position sensors have recently become increasingly common and accepted in human interfaces and for machine control. For example, in the fields of portable media players it is now quite common to find capacitive touch controls operable through glass or plastic panels. Some mobile (cellular) telephones are also starting to implement these kinds of interfaces.
Many capacitive touch controls incorporated into consumer electronic devices for appliances provide audio and/or visual feedback to a user indicating whether a finger or other pointing object is present or approaches such touch controls. A capacitive sensing microprocessor may typically be comprised in touch-controlled devices which are arranged to provide an “on” output signal when a finger is adjacent to a sensor and an “off” output signal when a finger is not adjacent to a sensor. The signals are sent to a device controller to implement a required function dependent on whether a user's finger is in proximity with or touching an associated touch control.
Some touch-controlled devices remain “on” or “active” despite the user having moved away from the device or a particular function no longer being required. This results in the device consuming a large amount of power which is not efficient.
There is therefore a need for an improved capacitive touch sensor which can regulate power usage.